LORE: all long lore is done by reznov that take's over from my short not great lore.
update, as of 04/10/2024 so awhile ago reznov moved on from coh-2 and no longer wants to do lore, im sorry if you liked his style but he's gone now, lore that was from him is the UNSC, 75th rangers and osttruppen force's lore.

OKW:
UNSC Faction: "Amidst the encroaching advance of the allied forces, the German Reich fervently endeavors to forge innovative technologies in their bid for victory in the failures of war. Yet, amidst this turmoil, an unforeseen anomaly emerges'a portal, within proximity to Berlin, bridging realms with the Halo timeline. In a surreal twist of fate, the UNSC forces, guardians of distant worlds, align themselves with the German Reich, harnessing their otherworldly arsenal to crush their enemies with absolute power."

USF:
75th Rangers: The 75th Rangers stand as a legendary force. Masters of reconnaissance, front line assaults, and breakthrough tactics, they wield diverse weapons with expert marksmanship and adaptability. Infamous for their tank-busting prowess and relentless pursuit of excellence, they evolve through combat experience, innovations, and specialized training, leaving an legacy of valour and sacrifice on the battlefield.

Wehrmacht:
Osttruppen Forces: "In the wake of the Allies' resurgent momentum, desperation grips the German Reich, driving them to drastic measures. With the tides of war shifting against them, the Reich marshals its allies and subjects, conscripting all within its grasp into a relentless struggle against the advancing forces of the enemy, heedless of the toll exacted. Thus is born the Osttruppen Forces, forged in the crucible of adversity to staunchly oppose the inexorable march of their adversaries, regardless of the sacrifices demanded."

Soivets.
GLA: with the German's pushing Russia back to Stalingrad resort to useing partisan's, and behind the line unit's and force's to attack the enemy with the Global Liberation Army and later deploy feared unit's like jerman kell and the stolen overlord tank from china.

british.
GDI: having fought off both NOD and scrin force's away from the last Threshold Tower and building up around it and then it opening up and recon squad's sent through, they find them self's in the mid of WW-2 but... not the same.

if you want the full non-summarised versions of the Lore here's the google document for that.
https://docs.google.com/document/d/12ZkGBbasj9YhzZXaYcGq7tfMcfa1wIfKdvyyQ2RZUUk/edit?usp=sharing